1. Field of the Invention
The invention relates to a strip of an adhesive film for a bond which is redetachable without leaving a residue.
2. Description of the Related Art
DE 33 31 016 C2 discloses adhesive films for redetachable (or temporary) adhesive bonds, which allow an adhesive bond produced therewith to be separated by pulling on the adhesive film in the direction of the bond plane. By means of adhesive films of this type, high adhesive forces and shear strengths can be achieved and adhesive bond systems can be separated again without further means, in comparable manner to the opening of a zip fastening or, better still, to the opening of a preserving jar: the rubber seal is pulled out of the sealing join via the grip tab. In practice, however, considerable disadvantages have become evident with the use of such adhesive films. Firstly, the product requires explanation. Any person not having previously used such an adhesive film is quite liable to bond the parts, which are to be joined, to one another in such a way that the adhesive film disappears between the joined parts, no longer protrudes and is therefore no longer able to be pulled on: the result is an irreversible bond with the attendant disappointment. The disappointment, however, is just as great if the adhesive film is used correctly but then, when pulled, tears: here too, an irreversible bond is the result. The advantage of an adhesive bond which can be redetached without damaging the joined parts in a very simple manner just by pulling is transmuted into a drastic disadvantage, since precisely those joined parts which were to be separated again are now permanently bonded. Often the only solution is to destroy the joined parts. The problem of tearing on pulling was recognized by the inventors of DE 33 31 016 C2, who paid particular attention to it. Accordingly, in the middle of page 4, a specific ratio of pulling force to tearing load is indicated: the tearing load should always be greater than the pulling force and for reliability the ratio of pulling force to tearing load should be from 1:2 to 1:3.
In practice, however, it has been found that this precautionary measure is in many cases inadequate. A bond of substrates on an open-air exhibition site, which is to be separated again after the end of the exhibition, can no longer be separated owing to tearing. The same is true, for instance, of calendars or advent decorations stuck to a window. Posters or pictures, too, fastened in this way to a wall, irreversibly become part of the decoration of the wall as soon as the adhesive films tear on pulling. The damage is considerable, the customer lost. Moreover, the use of even thicker adhesive films, as recommended in DE 33 61 016 C2, is unable to prevent such tearing. In addition, DE 37 14 453 C1 discloses the use of such an adhesive film, referred to therein as a strip tape, to enable the non-destructive removal of practice explosive charges from practice objects. Here too, a tab 6 is left projecting laterally from the adhesive join so that this tab can be pulled and the bond system separated again in this way. In this application, as well, tearing occurs in practice.
This problem of tearing is recognized by DE 42 22 849 C1, which proposes the application, on that end of the adhesive film which is pulled, of a UV-impermeable cover as grip tab. The intention thereby is to avoid from the outset damage to the adhesive film initiated by UV rays; it is from sites of such damage that a tear can be formed on pulling and can propagate. Nevertheless, even with these adhesive films tearing occurs. Similarly, DE 42 33 872 C2 describes a redetachable self-adhesive hook which has a UV-impermeable grip tab on the adhesive film. Here too, tearing occurs.
WO 92/11333 describes adhesive films for corresponding applications, which films comprise a backing film which combines low elasticity with high elongation. In such products, the tear-resistant backing film means that the problem of tearing does not occur, in contrast to the above-described products which consist purely of adhesive composition without a backing film.
The object of the invention was to remedy this situation. This is because the problem of tearing constitutes a central problem for adhesive films which purely comprise adhesive composition and do not have a backing film.
This object is achieved by adhesive film strips as characterized in more detail in the patent claims.
The fundamental construction of the adhesive strips according to the invention, and application-related dimensions, are described in detail in DE 42 22 849 C1, DE 33 31 016 C2 and DE 42 33 872 C2 for adhesive compositions and cover papers/cover films and can be employed equally for the present adhesive film sections according to the invention.